1. Field of the Invention
This invention relates to an apparatus for processing a photosensitive element and, more particularly, for processing an aqueous developable photosensitive element which contains colorant.
2. Description of Related Art
Reproduction of color images through printing is an involved process requiring a breakdown of an original image into a number of fundamental single color images and the eventual recombination of the single color images through multiple printings into a full color reproduction of the original. Color image reproduction typically includes the following steps.
First, using filtering and other photographic techniques a number of color separation transparencies or color separations are produced, typically four, each bearing a halftone dot and/or a continuous tone (contone) image corresponding, for instance, to magenta, cyan, yellow and black portions of the original. Second, a printing plate is made for each color separation by exposing a sensitized plate through one of the transparencies and developing the plate. Third, the printing plates are mounted on a multistage printing press which prints inks on a substrate, typically paper, sequentially and in register, one on top of another, four halftone and/or contone images corresponding to each of the color separations to create a full color reproduction of the original.
In the case of halftone images, the various colors are reproduced by the superposition of a multiplicity of dots of varying diameters and colors corresponding to the four color separations. Any deviation in the size or position of the printed dots results in color shifts in the final printed image. As a result of this reproduction process, setting up the press and printing a four color image is economically feasible typically only when employed for printing large quantities of a given original.
It is desirable to be able to predict the final image appearance before it is printed, and preferably before making printing plates by reviewing images made directly from the color separation transparencies. The art of evaluating the color separation transparencies and deciding whether the various colors have indeed been properly separated is called proofing. Proofing is a process which uses the color separations to create a colored image called a proof to visualize what the final printed image will look like typically without actually making printing plates and running the printing press. Proofing through the creation of proofs shows the printer and customer what the job will look like after printing, so changes can be made, if necessary, to the color separations before the job goes to press where it can waste expensive press time, paper and ink if it is not right. Proofs are used for many purposes including for customer approval, for checking compatibility of a number of subjects to be printed on the same plate or job, for internal quality checking and control, and for relatively small numbers of final reproductions.
For many years the only way to make proofs was to print them on a press. This involved making plates, mounting them on the press, making the press ready to run, and running a few prints. Proofs of this type are very expensive because they involve labor intensive operations and the use of expensive materials (e.g., plates) and cost intensive equipment (e.g., the press). Special proof presses have been built to eliminate the high costs of using production presses, but manpower costs are still high and special proof presses do not always reproduce the printing and visual characteristics of the production press. Furthermore, press proofing by either of these techniques takes a long time to make proofs.
Because of the time and expense to make press proofs attempts have been made to develop and use less expensive and faster alternatives to press proofs. These are usually made by photochemical or photomechanical means and are referred to as off-press, pre-press or pre-plate proofs.
Photochemical or photomechanical proofing systems typically use photosensitive elements in making proofs. These systems generally make proofs by exposing photosensitive elements to actinic radiation through one of the image bearing color separation transparencies to produce a duplicate image that is either a positive or a negative of the transparency depending on the element used. The radiation may make soluble areas insoluble, insoluble areas soluble, tacky areas nontacky, or nontacky areas tacky depending on the element used. After imagewise exposure, the photosensitive element can be developed by washing out soluble areas. Then tacky areas of the element may have to be toned with a dry or liquid colorant. This process is repeated for all color separations. Then the processed elements are laminated together one at a time sometimes on a support or substrate. Protective layers may be peeled apart and removed from the elements before they are laminated to the support or other image elements. Finally, the four color images may be transferred from the support to a receptor or transfer sheet, such as a sheet of paper, to form the final proof.
Many photosensitive elements used for image reproduction have the disadvantage that they must be washed out by an organic solvent or aqueous base. For instance, U.S. Pat. No. 4,053,313 to Fan discloses a photosensitive element comprising a solvent-processable photosensitive layer, a tonable elastomeric layer and a support, that is processed (i.e., washed-out) by a mixture of water and organic solvent. The elements disclosed in U.S. Pat. Nos. 4,376,158 and 4,376,159 to Speckler require aqueous base for washout. Precolored diazo based photosensitive elements which are developed in a mixture of 1-propanol and water are disclosed, for example, in U.S. Pat. No. 3,671,236 to Van Beusekom, U.S. Pat. No. 4,656,114 to Cederburg and U.S. Pat. No. 4,666,817 to Sachi. Use of organic solvents or aqueous bases frequently is undesirable due to flammability, toxicity, corrosion and/or waste disposal considerations. The photosensitive elements disclosed in these Fan and Speckler Patents also require the developed (i.e., washed-out) elements to be toned either manually or in a toning apparatus.
Photosensitive elements are known and are being developed that do not have the above described disadvantages. Specifically, U.K. Patent publication GB 2144867 B discloses photosensitive elements having entirely aqueously developable precolored layers containing a colorant on a removeable support. The U.K. Patent further describes a photomechanical process for forming a multicolor image, suitable for use as an off-press proof utilizing the aqueously developable photosensitive elements. The process for preparing a multicolor image is accomplished by (1) imagewise exposure of a first one of the precolored photosensitive elements comprising an aqueously developable precolored photosensitive layer on a removeable support through a first one of the color separation transparencies forming image areas and non-image areas in its aqueously developable precolored layer, (2) processing the exposed element to develop the color image by washing away the non-image areas with water, (3) laminating the image bearing element to a substrate, and then (4) peeling the removeable support from the image bearing element. A second color image element is made by exposing a second precolored photosensitive element with a second one of the color separation transparencies, processing to develop the color image, laminating in register the second color image element to the first color image element on the substrate and peeling the removeable support from the second color image element. By repeating the exposing, processing, laminating in register, and peeling steps two more times, a four color image can be obtained. As long as the emulsion layer of the color separation contacts the photosensitive layer in the photosensitive element during the exposure step as is preferred, the process described in this U.K. Patent results in a wrong reading proof on the substrate. This means that the image on the substrate is a mirror image of that captured in the color separations.
Often it is desirable to view the multicolored image on a receptor or a transfer sheet, such as paper, which is the same as or similar to that which will be used in the final printing run. In this case, the multicolor image is transferred to the desired receptor by laminating and then peeling away the substrate. This results in a right reading proof assuming the emulsion layer of the color separation contacts the photosensitive layer in the photosensitive element during the exposure step. A right reading proof is the same as the original image, not a mirror image.
Many apparatuses have been developed for developing photosensitive elements. Different developing apparatuses are designed and used for processing different photosensitive elements. However, aqueously developable precolored photosensitive elements are a relatively recent development. As such, few apparatuses exist for use in developing (i.e., washing out) non-image areas of aqueously developable precolored photosensitive elements.
Generally, the exposure of aqueously developable photosensitive elements through color separation transparencies form hardened and non-hardened areas corresponding to image and non-image areas on the photosensitive elements. The colored image produced after processing should have the non-hardened areas, i.e., non-image areas, and the colorant contained therein, completely washed-out or essentially completely washed-out. Any remaining non-hardened areas on the photosensitive element may affect the ability of the image bearing element to successfully transfer in lamination to the substrate. Also, any colorant which remains as a result of incomplete washout of the non-hardened areas deters from satisfactory resolution of the colored image. Thus, the apparatus for processing the photosensitive element should assure complete or essentially complete washout of the non-image areas and yet not be so harsh that it causes damage to the image areas on the element.
In accordance with the above, it is desirable to have an apparatus for processing photosensitive elements to develop an image on a support.
It is an object of this invention to provide an apparatus for processing by washing out non-image areas of a pre-exposed aqueously developable precolored photosensitive element to develop an image on a support.
It is another object of this invention to provide an apparatus for processing a pre-exposed aqueously developable photosensitive element which assures complete or substantially complete washout of the non-image areas of the photosensitive element so that optimum quality and performance of a color reproduction system is ensured.
These and other objects of the invention have been achieved in the present invention as will be clear from the following description.